- Technology explained – technology and procedures
Oil analysis: what the lab finds in the oil before the machine fails
By Tobias Schott · 5-minute read · Updated November 2026
Oil analysis reads in the lubricant what is happening in the machine – which components are wearing, what has got in from outside and whether the oil itself can still do its job.
You come across oil analysis in the lubrication schedule, in the maintenance contract or as a lab report with dozens of figures and a traffic light. For hydraulics, gearboxes, compressors and engines it is the machine’s blood test: a small sample bottle says more about the internal condition than a look through the sight glass.
This article explains how the sample is taken, what the lab measures and how to read the report. Which oil belongs where is covered in our article on oil viscosity; when to change it, in the guide on the lubrication schedule in maintenance.
What is oil analysis?
Oil analysis is the laboratory testing of a lubricant sample for wear particles, contamination and the condition of the oil itself. The oil runs through every bearing, gear and valve and picks up whatever is worn away there. It also carries what gets in from outside: dust, water, coolant, the wrong oil.
A single analysis is a snapshot. It only becomes valuable as a series: sample after sample, taken at the same point, it shows whether damage is developing. In German the method is called “Ölanalyse”; tracking it over time is known as oil condition monitoring.
Key facts
- Purpose: Detect wear, contamination and oil ageing before they lead to damage or an unnecessary oil change.
- Sample: A small amount of oil in a clean sample bottle, taken from the running or warm plant, always at the same point.
- Typical plant: Hydraulics, industrial gearboxes, compressors, turbine and circulating systems, diesel engines of generator sets.
- Measured values: Viscosity, water, particles and cleanliness class, wear and foreign elements, additives, ageing.
- Result: Lab report with measured values, comparison with the previous sample and assessment.
- Standard: ISO 4406 for the cleanliness class; limit values are set by the lab and the machine manufacturer.
- Common misconception: “A drain plug sample is representative” – it is not: sludge and water collect there.
The sample: where most mistakes happen
Oil analysis is only as good as the sample – a wrongly taken sample shows a condition the machine does not actually have.
- Take it warm. At standstill, particles and water settle. The sample should come from plant that is running or has just been shut down and is still warm.
- At the right point. Ideally via a sampling valve in the return line upstream of the filter. That is where the oil flows that has just passed through the machine.
- Flush first. Let the standing oil in the valve or hose run off first, then fill the bottle.
- Work cleanly. A new, clean bottle, no rags, no funnel from the workshop box. A single grain of dust distorts the cleanliness class.
- Always the same. Same point, same operating state; asset number, date, operating hours and oil grade on the label.
What the lab measures – and what the values reveal
The lab answers three questions: what is wearing in the machine, what has got in from outside, and can the oil keep running?
| Measured quantity | Typical source or meaning | Question for the plant |
|---|---|---|
| Iron | Gears, shafts, rolling bearings, cylinders and pump parts | Which steel part is wearing? |
| Copper, tin, lead | Bushes, plain bearings and bronze parts; copper also from coolers | Is a plain bearing or worm wheel wearing in? |
| Chromium | Piston rings, chrome-plated piston rods, alloyed bearing steel | Is a cylinder or bearing wearing? |
| Silicon | Usually dust, i.e. a leaking breather or seal | Where is dirt getting in? |
| Water | Condensation, cleaning, leaking cooler | Is a cooler or seal leaking? |
| Sodium, potassium, boron | Signs of coolant in the oil, especially in engine oil | Is a seal to the coolant circuit defective? |
| Particles and cleanliness class | Wear debris and dirt, counted by size | Is the filtration adequate? |
| Viscosity | Ageing, mixing with another oil, dilution | Is the right oil still in the plant? |
| Ageing and additives | Oxidation, depleted additives such as zinc, phosphorus or calcium | Can the oil keep running? |
The lab usually determines the metals by spectral analysis in milligrams per kilogram. It measures the water content by the Karl Fischer method. The cleanliness class to ISO 4406 is given as three numbers in a row, for example “18/16/13”. They indicate how many particles of four, six and 14 micrometres and above float in one millilitre. Smaller numbers mean cleaner oil.
Reading the report: trend before limit value
A lab report is read together with the previous sample, not on its own – what matters is what has changed.
If iron rises from sample to sample while silicon stays the same, a steel part is wearing from the inside. If silicon and iron rise together, ingressed dust is grinding. If copper suddenly appears, it is worth looking at bushes and coolers. These combinations are more valuable than any single value.
The traffic light in the report is based on limit values set by the lab and the machine manufacturer. Amber means: look more closely, resample, find the cause. Red means: act. An oil change alone only removes the symptom. If a seal lets water in, the new oil will soon be just as wet.
What we pay attention to
We take samples where the customer wants them and carry out repairs based on the lab findings.
- We take samples warm, at the same point and with clean tools – otherwise better not at all.
- We read the report together with the last one. A value without comparison is a number, not a finding.
- With water, dust or coolant, we look for the point of entry: breather filter, shaft seal, cooler, cleaning water.
- When wear metals rise, we check the component they point to – before the next oil change.
- After a repair we flush and clean so that old wear debris does not keep working in the new oil.
- We fill only the approved oil and record every change so that the next sample stays comparable.
Where we use it
The value of oil analysis shows most clearly in hydraulics, where pump, valves and cylinders depend on clean oil. Take the conversion of a servo-hydraulic test rig – we adapted the hydraulic lines and welded a continuous, leak-tight oil sump around the foundation. A simple rule applied there: oil must never escape uncontrolled. Drain cocks allow the oil to be drained into a container in a controlled way. Work like this is part of our Maintenance and servicing.
More technology explained
Technology explained
the oil type and its designation shown at the top of the report.
Technology explained
the method that shows the same bearing damage from the outside.
Guide
the guide to oil cleanliness, filters and leaks.
Do you have questions about how this works on your site?
Questions about how this works in your plant – for example, what the amber value in your oil report means for the plant? We find the cause, carry out the repair and make sure the next sample stays comparable. Request a callback – we will get back to you.
Free, no-obligation callback
About the author
Tobias Schott
Managing director of Omega Mounting GmbH, Rodgau · more than 20 years of hands-on experience in installation and maintenance
A trained mechatronics technician, working in maintenance, servicing and industrial installation since 2004 – first alongside his father, and with Omega Mounting since 2012: from overhead conveyors in Frankfurt to the crane system in a new-build hall. He plans and leads lifting operations as an appointed person (AP) in data centers and on industrial sites in the Rhine-Main region, trains and examines operators of cranes, mobile elevating work platforms and telehandlers, and is a qualified occupational safety specialist. On jobs abroad he is known as the “German Troubleshooter” – the person you call when a site gets stuck. He learned what quality means from his father, not from a manual: Made in Germany as a standard for his own work, not a label. That is why quality comes first at Omega Mounting – ahead of speed and price. The Technology explained articles cover the equipment and techniques his team uses every day: what counts on site is in them – what only appears in the brochure is not.
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